Casting metal



Nov. 15, 1938. F. F. POLAND El AL CASTING METAL Filed June.29, 1935 2Sheets-Sheet l INVENTORS BY lflllfld l ATTORN Y 2 Sheets-Sheet 2 BYZ'arlE [indmrr ATTORN Nov. 15, 1938. F. F. POLAND ET Al;

CASTING METAL Filed June 29, 1935 Patented Nov. 15,

CASTING METAL Frank F. Poland, New Brunswick, and Karl A. Undner,Railway, N. J.

Application June 29,

8 Claims.

This invention relates to improvements in the continuous casting ofcopper and copper-base alloys.

It has long since been proposed to produce castings of indefinite lengthby introducing the liquid metal into a mold or die, cooling the metal byextraction of heat through the die walls and continuously wihtdrawingthe solidified metal. However, in spite of the vast amount of effortexpended along this line, in times past, the pro posal never met withsuccess. In fact, the results were so disappointing that other methodsand means, such as withdrawing the heat down the previously congealedcasting, were proposed in efforts to successfully cast the metal in acontinuous manner.

By reason of certain improvements provided by the present invention itis now possible to successfully cast copper or copper-base alloys in acontinuous manner by an operation in which the metal is caused tosolidify by extraction of the heat through the die wall.

As a result of long and varied experimentation and investigation, it hasbeen discovered that the principal reason for the repeatedlyunsuccessful attempts to continuously cast copper or its alloys byprocesses embodying the concept of extracting heat through the diewalls, was the failure to fully appreciate and properly evaluate theessential characteristics of the die or mold itself. Based upon thisdiscovery, it has now been found that in order to successfully castcopper in the manner contemplated that the material comprising the diemust possess certain characteristics.

Among these characteristics, our investigations have shown that the dieor mold material must be one which is not only refractory and which willtake an extremely smooth finish but it must also possess a fair degreeof heat conductivity and remain stable with respect to thermal changeand shock. Further it must be non-wettable with respect to the metal, 1.e., it must act in a manner similar to that exhibited by mercury andunlike that exhibited by water in a glass tube, and it must be of aparticle size not exceeding 40 microns and of a porosity of not morethan 20% with pore spaces of 40 microns maximum. It will be understoodthat the figures relating to par icle size, porosity and pore space aremaximum and that lower figures are preferable if the material meets theother characteristics.

Although the novel features which are believed to be characteristic ofthis invention will be particularly pointed out in the claims appended1935, Serial No. 29,064

hereto, the invention itself, as to its objects and advantages, and themanner in which it may be carried out, may be better understood byreferring to the following description taken in connection with theaccompanying drawings forming a part thereof, in which- Fig. l is anelevation in section of one form of apparatus for practising theinvention,

Fig. 2 is an elevation in section of the die shown. in Fig. 1,

Fig. 3 is an elevation in section of a composite die, and

Fig. 4 is an elevation in section of a somewhat different die.

Referring now to the drawings, there is shown a furnace i0 mounted onplatform l2 supported by beams l4. Mounted upon refractory blocks [6 isreceptacle I 8 for holding the molten metal 20. The furnace I0 is heatedby any suitable means (not shown) such as oil or gas burners or electricheating means.

Extending downwardly from the bottom of the receptacle I8 and fittedtherein is the mold or die 22 having a channel or passageway 24 andsurrounded by cooling jacket 26 appropriately connected with coolingfiuid inlet 28, overflow tube 30 and outlet 32. A plate 34 defineschamber 36 directly beneath the mold 22 and gas inlet 38 leads to thechamber 36. Rolls III are provided for withdrawing the metal from themold as it solidifies.

As previously stated, the die or mold must be of material possessingcertain definite characteristics and standards. Among the materialsembraced by the invention are boron carbide (B40) and graphite ofextreme density, it being borne v in mind that the latter is not to beconfused with ordinary graphites or even graphites which are ordinarilyreferred to as dense and which are inoperative in the present process.In other words, only such graphite as will meet the spe-' cificrequirements heretofore referred to are contemplated.

Utilizing a material which falls within the specifications already setforth, however, the construction of the die or mold may be greatlyvaried and several variations in construction are shown in theaccompanying drawings. In Figs. 1 and 2 there is shown a relativelysimple mold construction comprising a die 22 having collar 42countersunk in the bottom of the receptacle l8. The channel 24 of thedie tapers slightlyto facilitate the ready withdrawal of congealedmetal. Surrounding the mold is jacket 26 adapted for the circulation ofwater or other cooling fluid from the inlet 28 to outlet 32 via overflowII.

Inasmuch as the most important consideration from the standpoint of thedie is the surface which contacts the metal in the congelation zone, itis only necessary to utilize material having the characteristicsheretofore enumerated for the lining of the mold. This allows theremainder of the mold to be made of other material thus permittingsubstantial savings in cost. Composite dies may thus be provided asillustrated in Figs. 3 and 4.

Referring to Fig. 3, there is shown a mold in which only the liner 44 isof material contemplated by the invention, the main body 46 of the moldbeing, for example, ordinary dense graphite. The liner 4 is secured inthe body portion 48 by threads 50. Between the bottom of the receptacle48 and the top of the cooling jacket-I6 is a mica sleeve 52 surroundedby a heating coil 54 enclosed in insulation 58, thus permitting asubstantial superheat to be imparted to the metal just prior to itschilling which has been found of value in improving the quality of thecast metal. The composite die shown in Fig. 4 is similar to that shownin Fig. 3, the heating coil and insulation being omitted.

In operation the bottom of the die or mold is closed with a suitableplug prior to the introduction of the metal into the receptacle l8 in amanner similar to that shown in Trotz U. S. Patent No. 705,721. Theclosing device may appropriately comprise a rod of the same diameter asthe desired casting and it preferably extends through the rolls 40 thusfacilitating the withdrawal of the rod at the start of the castingoperation.

The copper or copper alloy to be cast is then introduced into thereceptacle i8 and maintained in the proper liquid condition therein. Asuitable cooling fluid. such as water, is circulated through the jacketsurounding the die to congeal the metal in the mold. The metal firstentering the mold will weld to the closing plug and at the appropriatetime a longitudinal movement is imparted to the starting rod thuswithdrawing the casting from the mold. As the casting is withdrawn,additional metal is congealed above thus providing a casting ofcontinuous length. Nonoxidizing gas, such as illuminating gas, ispreferably introduced into the chamber 38 through the inlet 38 toprevent oxidation of the mold assembly which in some instances wouldotherwise be considerable at the temperatures employed.

The following specific examples of actual operations will serve toillustrate how the invention may be practised.

Example 1 Inthis instance a die of very dense graphite comprisinggraphite formed by chemical precipitation and cemented under highpressure with colloidal carbon as the bond, was used. The castingassembly was of the type illustrated in Fig. 3 with a nickel-chromiumcoil encircling the die between the receptacle and the water jacket. Themain body portion of the die consisted of ordinary dense graphite. Thetotal length of the die was seven and one-half inches with the dieproper, of material possessing the essential characteristics heretoforeenumerated, extending for a distance of approximately five and twotenths inches downwardly from the upper portion of the die. The top ofthe water jacket was three and seventy-five hundredths inches from thetop of the die, which latter had a diameter of one and one-half inches.

At the start of the run the copper had a temperature of 2140 F. and waswithdrawn at the rate of one and l four tenths inches per minute.Thereafter the temperature of the copper was increased to approximately2175" l". and the rate of withdrawal increased to approximately threeinches, which conditions were maintained until the end of the run. Themetal produced was found to be thoroughly sound, of excellent surfaceand composed of angular crystals disposed at an angle of approximately45.

Example 2 Using a construction such as shown in Fig. 4 with a one inchdiameter die tapering at the rate of 0.25 inch per foot, molten copperat 2125 F. was withdrawn at the rate of approximately two inches perminute, which rate was gradually increased to four and three tenthsinches per minute and continued until the end of the run. Thetemperature of the continuously cast rod, which was of excellent surfaceand sound throughout, was approximately 1800" F. as it emerged from thedie. An examination of the casting showed that with speeds of withdrawalbelow three inches per minute the crystals were angular but withwithdrawal speeds above that figurethe crystal structure was radial.

Example 3 Employing a mold of the type shown in Fig. 4 in which fourinches of the die insert was surrounded by the cooling jacket,phosphorus copper comprising approximately three and one-half pounds 01'phosphorus per ton of metal was cast at a temperature of 2210 F. with awithdrawal rate of three inches per minute, the temperature of theemerging rod being approximately 1565 F. The rate of withdrawal wasincreased to a speed of six inches per minute employing a metaltemperature of 2060 F. with the emerging cast ing exhibiting atemperature of 1670 F. The casting thus continuously produced was soundthroughout and exhibited an entirely radial crystal structure. a

It will thus be appreciated that by employing a die having thecharacteristics heretofore described, copper or copper-base alloys maybe successfully cast continuously in operations embodying the principleof heat extraction through the walls of the mold or die. It may also beadded that in addition to forming the die (at least that part contactingthe metal) from material which will meet the standards specified, it isalso preferred to provide a slight taper for shapes less than about twoinches in diameter to assist in the withdrawal of the castings. Incasting larger shapes, for example, billets of three inches or more indiameter, the taper may well be dispensed with as the contraction of thecopper upon solidification is suiilcient to provide adequate clearance.

It is not at present exactly known why the material from which the dieis formed must have the characteristics which have been found soessential but it is possible that the productionof radial or angularcrystals such as are formed when the heat is withdrawn through the diewall, set up conditions which do not exist in the case of longitudinalcrystallization. Whatever the explanation, however, it is clearlydemonstrated by the invention that the use of a polished die made frommaterial of the class described, such as boron carbide or exceedinglydense graphite permits the continuous casting of copper by processes inwhich the heat is extracted through the die wall by a surroundingcooling medium.

While certain novel features of the invention have been disclosed andare pointed out in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A process for continuously casting metal which comprises supplyingthe metal to a mold formed of refractory, heat-conducting material whichis non-wettabie with respect to the metal and which exhibits a maximumporosity and pore space of 20% and 40 microns respectively, circulatinga cooling fluid around the metal in said mold thereby withdrawing heatfrom the metal through the die walls and causing the metal to solidifyand withdrawing the cast metal from said mold. g

2. A process for casting metal which comprises continuously supplyingmolten metal to a mold having congealed metal in the bottom-thereof, theinner surface of said mold consisting of a refractory, heat-conducting.material of particle size not exceeding 40 microns and exhibiting notmore than 20% porosity, congealing additional metal to that present inthe bottom of themold by circulating a cooling medium around the moldand withdrawing the resulting casting as additional metal is congealedwithin the mold.

3. In the art of continuously casting copper, that improvement whichcomprises passing the copper through a die of refractory,heat-conducting material, non-wettable with respect to copper, theparticles and pore spaces 'of which do not exceed 40 microns andcirculating a cooling medium around said die thereby solidifying themetal by extraction ofheat through the die walls.

4. Metal casting apparatus comprising a receptacle for molten metal, arefractory, heatconducting die communicating with said receptacle and inwhich the metal is solidified, said die consisting of materialnon-wettable with respect to the metal being cast and having particlesand pore spaces not exceeding 40 microns and a maximum porosity of 20%and cooling means surrounding said die for the extraction of heatthrough the walls of the latter.

5. Apparatus for continuously casting copper comprising a reservoir formolten copper, a mold of boron carbide communicating with said reservoirand adapted to receive molten copper therefrom, means for circulating acooling fluid about said mold to effect solidification of copper thereinand means for withdrawing the cast copperfrom said mold as additionalquantities of same,

are congealed.

6. Apparatus for continuously casting copper andalloys thereofcomprising, a reservoir, a composite mold adapted to receive metal fromsaid reservoir and retain same until solidified, the

interior surfaces of said mold consisting of a sleeve of refractorymaterial non-wettable with respect to copper and of maximum particle.size and pore spaces of 40 microns with a porosity not exceeding 20%, acooling means associated with said mold for withdrawing heat through thewalls thereof and means for regulating: the rate of withdrawal of thecasting from said mold.

'7. Apparatus for continuously casting copper comprising the combinationwith a receptacle defining a reservoir for molten copper, of arefractory, heat conducting die communicating withv the receptacle forreceiving molten copper from the receptacle and defining a congelationchamber for the molten copper, the said die having at least its surfacewhich is in contact with the molten copper consisting of dense graphitehaving particles and pore spaces not exceeding 40 ceeding 20%. a

FRANK Fr POLAND. KARL A. LINDNER.

